Flaviviruses are small, enveloped positive-strand RNA viruses. Flavivirus proteins are produced by translation of a single, long open reading frame to generate a polyprotein, which is followed by a complex series of post-translational proteolytic cleavages of the polyprotein by a combination of host and viral proteases to generate mature viral proteins (Amberg et al., J. Virol. 73:8083-8094, 1999; Rice, “Flaviviridae,” In Virology, Fields (ed.), Raven-Lippincott, New York, 1995, Volume I, p. 937). The virus structural proteins are arranged in the polyprotein in the order C-prM-E, where “C” is capsid, “prM” is a precursor of the viral envelope-bound M protein, and “E” is the envelope protein. These proteins are present in the N-terminal region of the polyprotein, while the non-structural proteins (NS1, NS2A, NS2B, NS3, NS4A, NS4B, and NS5) are located in the C-terminal region of the polyprotein.
A chimeric flavivirus that includes the C and non-structural proteins of the Yellow fever virus vaccine strain (YF 17D) and the prM and E proteins of a strain of attenuated Japanese encephalitis virus (SA 14-14-2) has been made. This chimera, designated CHIMERIVAX™-JE (chimeric flavivirus comprising capsid and non-structural proteins from yellow fever virus and pre-membrane and envelope proteins from Japanese encephalitis virus), has been shown to induce the production of neutralizing antibodies against JE in immunized rhesus monkeys, as well as to protect these monkeys from clinical encephalitis after JE challenge, as compared with unimmunized controls. CHIMERIVAX™-JE (chimeric flavivirus comprising capsid and non-structural proteins from yellow fever virus and pre-membrane and envelope proteins from Japanese encephalitis virus) was shown to meet preclinical safety requirements for a human vaccine (Monath et al., J. Virol. 74(4):1742-1751, 2000).
A similar chimera was made that includes the C and non-structural proteins of YF 17D and the prM and E proteins of a Dengue-2 strain. This chimera, designated CHIMERIVAX™-D2 (chimeric flavivirus comprising capsid and non-structural proteins from yellow fever virus and pre-membrane and envelope proteins from Dengue-2 virus), was shown to induce neutralizing antibodies against Dengue-2 virus in rhesus monkeys, as well as to protect these monkeys from viremia after Dengue-2 challenge, as compared with unimmunized controls. CHIMERIVAX™-D2 (chimeric flavivirus comprising capsid and non-structural proteins from yellow fever virus and pre-membrane and envelope proteins from Dengue-2 virus) also was shown to be safe and genetically stable (Guirakhoo et al., J. Virol. 74(12):5477-5485, 2000).